Fluorescent molecular rotors are a class of fluorophores whose emission intensity is sensitive to the ability of the local environment to restrict bond rotations. Recently, these fluorophores have been used to study bacterial growth and development, however, the existing probes lack optimized physical and fluorescent properties for this type of application. To address this issue, new and existing fluorescent molecular rotors were synthesized and comparatively evaluated in an environment with increasing viscosity. Fluorescent molecular rotors were designed and synthesized from taking the previously reported structures with a tetrahydroquinoline core which was modified to include a methylpyridinium moiety. A pair of new molecular rotors was also synthesized by extending conjugation with 5-formylthiophene-2-boronic acid via Suzuki-Miyaura coupling. The study of newly synthesized compounds was carried out to determine stability in pH 7.4 buffer, red-shifted emission and excitation, and fluorogenic sensitivity to highly viscous environment. Pyridinium-based fluorescent molecular rotors showed comparable fluorogenic properties to established rotors, and also possess the desired red-shifted excitation and emission spectrums. Extended thiophene-based fluorescent molecular rotors improved the photophysical properties, however, ongoing viscosity sensitivity studies have provided inclusive results. Future studies will include the adjustments to the viscosity sensitivity assay to determine the molecular rotors properties of thiophene-based fluorescent compounds.

Synthesis and characterization of pyridinium-based fluorescent molecular rotors

ACS Spring 2022

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